GRAYLING OF GREBE LAKE 



343 



a. 

 A 



■H 



- Q ^ 



3 



10 11 02 13 U 15 



Total length in inches 



Figure 28. — Length-weight relation of 148 hybrid trout from Grebe Lake, Yellowstone National Park. 



average weight within each 1-ineh group. 



Dots represent 



can best be expressed by a parabolic curve of 

 the form W=cL", where 



W=weight of the fish, 



L= length of the fish, and 



c and n are constants. 

 Converted to logarithms, the formula becomes, 

 log W=log c+n log L, and the constants can be 

 determined by the method of least squares. 



Paired length-weight measurements of 148 

 hybrid trout were from two groups of individuals. 

 The first group was comprised of fish more than 

 6.0 inches long and contained both gill-net 

 captures of August 1952, and tagged males taken 

 during spawning runs. The second group was 

 composed of trout under 6.0 inches in length; 

 measurements of these were made on preserved 

 specimens originally seined from Grebe Lake. 

 Since only a limited number of measurements 

 were available for the two species, both sexes 

 were used in calculations (except no length and 

 weights were from spawning females of either 

 species). The 309 grayling used in computations 



were from gill-net captures (August 1952) (more 

 than 6.3 inches total length) and preserved speci- 

 mens (less than 6.3 inches). 



The calculated curves (figs. 28 and 29) fit the 

 empirical values very well. For the hybrid trout, 

 the predicted weights of fish follow the formula 

 log W T = 2.5420 log Z-0.9674 (fig. 28). In the 

 grayling the length-weight curve is of the form 

 log V= 2.7682 log L- 1.2925 (fig. 29). 



FOOD ANALYSIS 



The grayling and the hybrid trout compete for 

 food in Grebe Lake. The extent to which they 

 do this is disclosed in part by a comparison of 

 their stomach contents. 



Stomachs were taken from 112 grayling and 

 24 hybrid trout during 1952 to 1954. These 

 fish were captured with hook and line, by weirs 

 used during the spawning season, and by nets. 

 The stomachs were preserved in 5 percent formalin 

 as soon as possible after collection of the fish. 

 The total content of each was subsequently 



